(1) Field of the Invention
The present invention relates to a cooling system for an internal combustion engine, and more particularly to a cooling system which cools an internal combustion engine by flowing a coolant inside annular grooves provided to an outer surface of a cylinder.
(2) Description of the Related Art
Conventionally, there is disclosed a cooling system of a cylinder liner, for example in Japanese Laid-Open Utility Model Application No.63-168242. The cooling system disclosed in this Application includes a plurality of grooves for cooling formed on and along an outer surface of a cylinder liner in a direction roughly perpendicular to an axis of the cylinder liner. The system also includes two connecting grooves connecting these grooves and extending in the direction of the axis of the cylinder liner. The later grooves are positioned in 180 degree opposition from each other along a diameter of the cylinder liner. Continuing passages for coolant are formed between each of the grooves on the outer surface of the cylinder liner and the inner surface of a bore of a cylinder block by fitting the cylinder liner to the bore of the cylinder block.
In Japanese Patent Application No.3-51701, the applicant suggested a system as shown in FIG. 1 as a cooling system for an internal combustion engine as mentioned above, a so called groove cooling.
In FIG. 1, a plurality of square cross-sectioned annular grooves 3 are formed on an outer surface of a cylinder liner 2. The annular grooves 3 are equally spaced along a direction of the axis of the cylinder liner 2 which is fitted to a cylinder block 1. These annular grooves 3 form annular passages for a coolant between an outer surface of the cylinder liner 2 and an inner surface 4 of a bore of the cylinder block 1, when the cylinder liner 2 is fitted to the bore of the cylinder block 1.
Longitudinal grooves 5a, 5b and 6a, 6b connecting the grooves 3 are formed extending in a direction of an axis of the cylinder liner 2 in positions where the cylinder liner 2 and the cylinder block 1 face each other. In the cylinder block 1, inlet ports 7a, 7b, which are respectively connected to the longitudinal grooves 5a, 5b, and outlet ports 8a, 8b, which are respectively connected to the longitudinal grooves 6a, 6b, are formed.
A pump 9 for delivering a coolant delivers a coolant to two separate lines. Coolant going to one line is highly pressurized and supplied to the inlet port 7a via a filter 10. Coolant going to the other line is low pressure, and is supplied to the inlet port 7b directly. The coolant supplied to the inlet port 7a flows through the longitudinal groove 6a and outflows from the outlet port 8a, after flowing through the longitudinal groove 5a and being delivered to the annular grooves 3 in the upper part of the cylinder and flowing through the grooves 3. The coolant supplied to the inlet port 7b flows through the longitudinal groove 6b and outflows from the outlet port 8b, after flowing through the longitudinal groove 5b and being delivered to the annular grooves 3 in the lower part of the cylinder and flowing through the grooves 3. The coolant outflowing from the outlet ports 8a, 8b are joined together and are returned to the pump 9 via a radiator, not shown.
According to the system mentioned above, heat generated in a combustion chamber and transferred from a cylinder head to the cylinder liner 2 can be eliminated by cooling a wall of the cylinder liner 2. The wall of the cylinder liner 2 has an incoming heat distribution such that the incoming heat at the uppermost part of the cylinder liner 2, as in FIG. 1, is highest and degrades as it goes to the lower part. Therefore, it is required that the amount of coolant flow in the annular groove 3 closest to a combustion chamber is maximized and the flow decreases as it flows the groove 3 further apart from the uppermost groove 3, as indicated by c in FIG. 2, so as to uniformly cool down the wall of the cylinder liner 2.
In the system mentioned above, if a diameter of the longitudinal grooves 5a, 5b, 6a, 6b is larger than the predetermined size, a distribution of the coolant flow in the plurality of the grooves 3 is constant, as indicated by a in FIG. 2. However, by decreasing the diameter of the longitudinal grooves 5a, 5b, 6a, 6b, the coolant flow in the grooves 3 in the upper part can be relatively larger than that in other grooves 3, and thus the distribution of the coolant flow can be similar to the distribution of the incoming heat on the wall of the cylinder liner 2 indicated by c in FIG. 2.
However, in the system mentioned above, since the difference of the flow between the uppermost groove 3 and a lower groove 3 is too large, it is difficult to match the distribution of the flow to the distribution of the incoming heat. The cause of this problem is that the amount of the coolant flowing into the uppermost groove 3 is much larger than that flowing into the lower groves 3 because that the uppermost groove is located in a direction of the coolant flow and, on the contrary, the grooves 3 lower than the uppermost groove 3 are located perpendicular to the direction of the coolant flow, thus generating a pressure loss due to the bend in the direction of the flow. As a result, in the system mentioned above, the main part of the coolant flows in a direction as indicated by an arrow in FIG. 1.